New techniques have been developed in the laboratory for the purification of C3, 5, 6, 7, and C56 complex. New assays have been developed for the C3b inactivator and for the protein Beta 1H and has been shown rigorously that both of these proteins are required for C3 inactivation. The characteristics of this interaction which leads to the destruction of the opsonically active C3 site have been examined. Studies of the interaction of bacteria with the complement proteins have led to a understanding of the role of complement in the sequestration of bacteria and in the pulmonary localization of bacteria. It has been shown that C5a plays a key role in pulmonary localization of bacteria as well as in the development of the shock lung syndrome in animals with bacteriemia. The shock lung syndrome in man will be studied for similar effect.